Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more turbine rotor blades. The turbine blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines. One such modification has been to increase the length of the rotor blades. However, as is generally known, the deflection of a rotor blade is a function of blade length, along with wind speed, turbine operating states and blade stiffness. Thus, longer rotor blades may be subject to increased deflection forces, particularly when a wind turbine is operating in high-speed wind conditions. These increased deflection forces not only produce fatigue on the rotor blades and other wind turbine components but may also increase the risk of the rotor blades striking the tower.
In order to increase the length of wind turbine rotor blades without adversely affecting the aerodynamic design, it is known to install tip extensions onto the blades. Typically, a conventional tip extension is installed onto a rotor blade by cutting-off a portion of the blade at its tip and replacing such cut-off portion with the tip extension. However, due to the fact that a portion of the rotor blade must be cut-off and because the elongated rotor blade will be subjected to increased loads, the tip extension must be significantly longer than the actual increase in rotor blade length that can be achieved by installing the extension. For example, a conventional tip extension may often need to have a length of almost half of the original span of the rotor blade to accommodate the increased loading on the blade. As such, due to their length, the costs of manufacturing and transporting conventional tip extensions can be prohibitively expensive.
To address the aforementioned issues, it is known in the art to provide blade inserts to increase the span of the rotor blades. For example, U.S. Pat. No. 9,297,357 filed on Apr. 4, 2013 entitled “Blade Insert for a Wind Turbine Rotor Blade,” describes a blade insert configured to increase the span of a rotor blade by an amount generally corresponding to the overall length of the blade insert.
In addition, the '357 patent describes an access window defined between the insert and the blade segments to permit the ends of the blade insert to be secured to the joint end of each blade segment. Such access windows may generally allow for service workers to access the interior of the rotor blade, thereby allowing various components to be positioned within the rotor blade to facilitate securing the blade insert between the blade segments. Further, the access windows are covered by a window cover that is secured within the access window via a laminated connection.
Though the laminated connection sufficiently secures the window cover within the access window, it would be advantageous to bond the window covers in place (e.g. via a bonding agent). However, a bonded window cover, without a transition from two sets of inner skins to a single set of inner skins, would cause an undesirable bump at least at the leading edge of the rotor blade.
Accordingly, the present disclosure is directed to a bonded window cover and corresponding joint assembly that eliminates such an undesirable bump at the leading edge.